2002 Audi A6 front brake rotors were warped

My car is making a humming noise when I turn at low speeds (backing out of driveway, navigating through parking lots, etc.). I took it in twice and the first time they found the front brake rotors were warped so they replaced those and the noise went away for a few weeks but then started coming back again. I took it in a second time and they found corrosion around that area which they said can happen due to weather. So they hit the brakes hard a few times and the corrosion came off and the noise went away. I just got my car back the other day and I can still hear a slight noise again. Is there something else that may have been overlooked? I know that the car shouldn't be making any noises. Any help would be appreciated. Thanks.